Method for the production of a one-piece rotor area and one-piece rotor area

ABSTRACT

The present invention describes a method for the production of a one-piece rotor area, preferably of a jet engine. The rotor area includes an annular base body and several, circumferentially distributed blade elements extending essentially radially from the base body. Residual stresses are imparted to the blade elements in surface-near areas by way of roller compression using a rolling tool introduced between the blade elements. During roller compression, one each area of a blade element is arranged between areas of the rolling tool, with longitudinal sides of the blade element being simultaneously roller-compressed. According to the present invention, the rolling tool is radially introduced between the blade elements and the surfaces of the blade elements are roller-compressed, thus at least the blade elements having a roller-compressed surface.

This invention relates to a method for the production of a one-piecerotor area according to the type more precisely defined in the genericpart of patent claim 1 as well as to a one-piece rotor area according tothe type more precisely defined in the generic part of patent claim 9.

Downstream of a fan, jet engines known from practical applications areprovided with multi-stage compressors, in the area of which the coreairflow is incrementally increased to a desired pressure level. Theindividual compressor stages include blade elements or rotor blades ofone-piece rotor areas rotating during the operation of a jet engine andvane elements or stationary guide vanes corresponding therewith.

In the area of the non-rotating stators, mechanical loading isrelatively low during the operation of a jet engine since, on the onehand, rotation-due centrifugal loads do not exist and, on the otherhand, blade vibrations are minimized by the residual stress of the flowprofile in the root and top area.

However, high mechanical loading is present during the operation of ajet engine in the area of the rotor blades. Their total load is composedof several partial loads, with the centrifugal force being the dominantpartial load. Since the change of speed is only small during theoperation of a jet engine, the centrifugal force, which is superimposedby dynamic partial loads, can be considered as approximately static.

The dynamic partial loads result from the rotation-due vibrationexcitation of the rotor blades or the blade elements, respectively.Furthermore, the rotor blades are subject to aerodynamically causedloads which are primarily attributable to periodically non-stationaryflows. Generally, periodically non-stationary flows are due to thestator-rotor interaction generated by the splitting of the flow as therotor blades pass the stator vanes. Dynamic loads are further producedby interaction of the flow profiles with the turbulent flow, againresulting in blade vibrations. The dynamic partial loads, in total, leadto high-frequency vibrations occurring in operation primarily in thearea of rotor blades of compressors as well as fans or, generallyspeaking, one-piece rotor areas of jet engines, resulting in highlydynamic stressing of the rotor blades.

Besides mechanical loading, part of the blades is also subject tothermal loading. This applies primarily to the blades of thehigh-pressure compressor and the rearward blades of the low-pressurecompressor where operating temperatures up to 600° C. exist.

Generally, the blades of compressors or fans of jet engines are designedsuch that the fatigue strength is not, or only in a defined manner,exceeded by the dynamic operating loads and endurance strength or,respectively, a defined level of fatigue strength is ensured. However,premature crack initiation and sometimes even uncontrolled failure offan and compressor blades, which is predominantly attributable to bladedamage by foreign objects, are encountered time and again.

Such foreign object damage is impact damage resulting from theimpingement of hard foreign objects. The foreign objects are generallystones and fragments of bolts, nuts, washers and similar items lying onthe runway.

Foreign objects frequently fragment upon impingement. These fragments,as well as any object passing the fan area without collision, areentrained further into the engine by the airflow. If the engine featuresa large bypass airflow, part of the objects may leave the engine viasaid bypass airflow without causing any major damage. The other partenters the low-pressure compressor together with the core airflow,causing serious collision, primarily with the quickly rotating rotorblades. As a result of kinematics, the main damage location is, similarto the fan, in the area of the inflow edge and the forward concaveprofile side.

In order to protect the blade elements or, respectively, the rotorblades against foreign object damage and avoid any crack formationresulting therefrom in the area of the blades during the operation ofthe engine, it is required that the blade elements, as well as theannular base bodies forming an integral part thereof be conceived withsuitable solidity. The high material investment involved therewithhowever increases the total weight and also the manufacturing costs of ajet engine in an undesirable manner.

Therefore, a method of resolidifying rotor blades or blade elements,respectively, of jet engines has been adopted, using appropriatemanufacturing processes, and enabling rotor blades to be provided whosecomponent dimensions are smaller than those of non-resolidified rotorblades.

For this purpose, the rotor blades and annular base bodies forming anintegral part of the rotor blades are resolidified by means of shotpeening, with residual stresses being produced in the shot-peeningprocess in surface-near areas of the rotor blades counteracting crackformation and crack propagation due to foreign object damage orvibratory loading to the extent required.

It is however disadvantageous that the surfaces of rotor bladesresolidified by shot peening have inferior surface quality which must bere-improved after shot peening by elaborate and costly reworkoperations. Moreover, shot peening does not ensure a uniform processingof rotor blades or blade elements, respectively, of one-piece rotorareas, since—for example due to ricochetting or shielding effects—somesurface areas are hit by the shot more frequently than others, as aresult of which effects detrimental to service life, such asde-solidification, may occur and reproducible processing results are notensured. Solidification of one-piece rotor areas by means of shotpeening is therefore very imprecise and also cost-intensive as itinvolves the use of compressed air.

It is further known to roll rotor blades in certain areas by means ofpliers-type tooling, thereby generating residual stresses insurface-near areas of the rotor blades. In the process, a blade areafacing the flow is solidified by roller compression using a rolling toolin the direction of flow or in the axial direction, respectively. Here,usually approx. 20 percent of the surface of a blade element areroller-compressed by simultaneous, both-side rolling of the longitudinalsides in the direction of flow, starting at the leading edge of theblade element, thereby achieving or retaining a high surface quality andavoiding deformation of thin-walled profiles.

This process is, however, disadvantageous in that stress jumps occur atthe transition between the surface area of a blade element resolidifiedby roller compression and the non-resolidified surface area of a bladeelement. As the blade element is subject to vibratory loads, maximumstress limits are exceeded at this transition area so that plastic flowoccurs in the area between the processed area of a blade element and thesurface area not processed by roller compression which may result inundesirable crack formation. Cracks once produced will propagate underfurther vibratory load, ultimately leading to the failure of a bladeelement.

The present invention, in a broad aspect, provides a method for theproduction of a one-piece rotor area, preferably of a jet engine, bymeans of which one-piece rotor areas are producible with high resistanceto foreign object damage and vibratory loading and at the same time lowcomponent weight. In addition, it is an object of the present inventionto provide a one-piece rotor area which, while being cost-effectivelyproducible and having a surface with low roughness, is characterized byhigh resistance to foreign object damage and vibratory loading.

It is a particular object of the present invention to provide solutionto the above problematics by a method in accordance with the features ofpatent claim 1 and a one-piece rotor area in accordance with thefeatures of patent claim 9.

In the method according to the present invention for the production of aone-piece rotor area, preferably of a jet engine, including an annularbase body and several, circumferentially distributed blade elementsextending essentially radially from the base body, residual stresses areimparted to the blade elements in surface-near areas by way of rollercompression using a rolling tool introduced between the blade elements.During roller compression, one each area of a blade element is arrangedbetween areas of the rolling tool, with longitudinal sides of the bladeelement being simultaneously roller-compressed.

According to the present invention, the rolling tool is radiallyintroduced between the blade elements and the surfaces of the bladeelements are roller-compressed.

Roller compression of the surfaces of the blade elements enables aone-piece rotor area, preferably of a jet engine, including an annularbase body and several, circumferentially distributed blade elements, tobe provided with—as compared to non-resolidified rotor areas—lowermaterial investment and, thus, lower total weight while at the same timehaving equal or higher resistance to foreign object damage and vibratoryloading.

Moreover, roller compression of the surfaces of the blade elementsprovides a simple means of avoiding stress jumps and improving theresistance to vibratory loading as compared to blade elements that areresolidified only in certain areas.

As the rolling tool is introduced radially between the blade elements,high resistance to foreign object damage and vibratory loading caneasily also be provided to one-piece rotor areas having several bladeelements arranged axially one behind the other on the base body. Becauseof the small spacing between the individual blade element rows, this isnot possible using the known practices in which the rolling tool isaxially introduced between the blade elements.

In a variant of the method according to the present inventioncharacterized by low control effort, the surfaces of the blade elementsare roller-compressed by sequential radial traversing, at least incertain areas.

In a variant of the method according to the present invention, which isalso easily feasible, the surfaces of the blade elements are rolled bysequential axial traversing, at least in certain areas.

If the surfaces of the blade elements are roller-compressed byarbitrarily moving the rolling tool along the surfaces of the bladeelements at least in certain areas, the latter can be provided with asurface structure required for generating a homogenous flow around theblade elements.

In a further advantageous variant of the method according to the presentinvention, resistance of a one-piece rotor area is further increased inthat the transition areas between the surfaces of the blade elements andthe surface of the base body between the blade elements isroller-compressed using a rolling tool.

Resistance to foreign object damage and vibratory loading of a one-piecerotor area characterized by low weight can further be improved in thatthe surface of the base body between the blade elements isroller-compressed using a rolling tool.

In order to further improve durability of the blade elements, a furtheradvantageous variant of the method according to the present inventionprovides that a rolling force is variable to enable the surfaces of theblade elements to be provided with specifically the surface-nearresidual compressive stress which in each case is best for increasingthe resistance to foreign object damage and vibratory loading.

The one-piece rotor area according to the present invention features anannular base body and several blade elements distributed over thecircumference of the base body and extending essentially radially fromthe latter. Since at least the blade elements have a roller-compressedsurface, the one-piece rotor area according to the present invention—ascompared to non-resolidified or only partly resolidified one-piece rotorareas—is characterized by low weight while at the same time having atleast equal resistance to foreign object damage and vibratory loadingand, additionally, provided in the area of the blade elements in acost-effective manner, as no extra processing steps are required, with asurface characterized by high surface finish supporting homogenous flowaround the blade elements.

If also the joining areas between the surfaces of the blade elements anda surface of the base body are provided with a roller-compressedsurface, both resistance to foreign body damage and vibratory loading aswell as homogenous flow around the one-piece rotor area are ensured.

In another advantageous embodiment of the one-piece rotor area inaccordance with the present invention, resistance to foreign objectdamage and vibratory loading is improved in that the base body featuresa roller-compressed surface at least in the area between the bladeelements.

In a further advantageous embodiment of the one-piece rotor area,several blade elements axially arranged one behind the other on the basebody are provided with a roller-compressed surface.

Both the features cited in the patent Claims and the features specifiedin the following exemplary embodiment of the subject matter of thepresent invention are, alone or in any combination, capable of furtherdeveloping the subject matter of the present invention. The respectivecombinations of features are in now way limiting the development of thesubject matter of the present invention, but essentially have onlyexemplary character.

Further advantages and advantageous embodiments of the subject matter ofthe present invention become apparent from the patent Claims and theexemplary embodiment schematically described in the following withreference to the accompanying drawing. In the drawing,

FIG. 1 shows a highly schematized longitudinal sectional view of a jetengine provided with a one-piece rotor area,

FIG. 2 is an enlarged individual representation of a blade element ofthe one-piece rotor area as per FIG. 1,

FIG. 3 is a side view of a rolling tool, and

FIG. 4 shows the rolling tool as per FIG. 3 in a view IV represented inmore detail in FIG. 3.

FIG. 1 shows a longitudinal sectional view of a jet engine 1 providedwith a bypass duct 2. The jet engine 1 is further provided with an inletarea 3 downstream of which a fan 4 is arranged in known manner. Againdownstream of the fan 4, the fluid flow in the jet engine 1 divides intoa bypass flow and a core flow, with the bypass flow passing through thebypass duct 2 and the core flow into an engine core 5 which, again inknown manner, is provided with a compressor arrangement 6, a burner 7and a turbine arrangement 8.

FIG. 2 shows an enlarged individual view of a one-piece rotor area 9 ofthe compressor arrangement 6 including an annular base body 10 andseveral circumferentially distributed blade elements 11 extendingessentially radially from the base body 10.

The one-piece rotor area 9 is a so-called blisk, i.e. an integrallybladed rotor design. The term blisk is composed of the words “blade” and“disk”. The disk or, respectively, the annular base body 10 and theblade elements 11 are made in one-piece, removing the need for bladeroots and disk slots provided on multi-piece rotor areas. The one-piecerotor area 9 is distinct from conventionally bladed compressor rotors bya significant decrease in the number of components and the disk shape ofthe annular base body 10 is designed for lower rim loads. In combinationwith the use of lighter materials, this results in a weight saving ofthe one-piece rotor area 9 of up to 50 percent compared to conventionalrotor areas. The amount of weight saving is in each case dependent onthe geometry of the compressor arrangement 6.

A further positive effect is that the blade elements 11 of theintegrally bladed rotor area 9 are spaceable more closely to each other,thereby enabling best possible compression and enhancement ofefficiency.

In order to provide the compressor arrangement 6 or, respectively, theone-piece rotor area 9 with resistance to foreign object damage and alsovibratory loading while at the same time keeping the weight low,residual stresses are imparted to the blade elements 11 in surface-nearareas by way of roller compression using a rolling tool 14 radiallyengaging in each case between the blade elements 11 and further shown inFIGS. 3 and 4, with the entire surface of each blade element 11 beingroller-compressed in each case. Additionally, the transition areas 12,or fillets, respectively, between the surfaces of the blade elements 11and a surface 13 of the base body 10 between the blade elements 11 arealso roller-compressed by means of a so-called one-finger rolling toolnot further shown in the drawing.

Furthermore, the surface 13 or, respectively, the annulus of the basebody 10 between the blade elements 11 is preferably alsoroller-compressed by means of a one-finger rolling tool.

Roller-compressing the surfaces of the longitudinal sides and the edgesof the blade elements 11, the transition areas 12 and the surface 13 ofthe base body 10 in each case solidifies surface-near areas of theone-piece rotor area 9 by increasing dislocation density and hardens thesurface layer of the rotor area 9. Hardening the surface layer reducesthe risk of cracking resulting from foreign object damage and vibratoryloading. Moreover, the residual compressive stresses imparted by rollercompression to the material in the area of the rotor area 9 counteractcrack propagation after crack formation, thereby positively influencingfatigue strength and, thus, the service life of the jet engine 1.

Furthermore, roller compression provides the one-piece rotor area 9 withhigh surface finish and low surface roughness, thereby positivelyinfluencing the aerodynamic quality of the blade elements 11 and theentire rotor area 9 without the need for a further surface smootheningprocess to be performed subsequently to the solidification process.

FIG. 3 and FIG. 4 each show a side view of a rolling tool 14 forroller-compressing the longitudinal sides or, respectively, the entiresurface of the blade elements 11 of the rotor area 9. The rolling tool14 includes a tool carrier 15, which can be connected to a carrierspindle 16 of a machine tool to the extent shown. Two pliers-type bodies17, 18 of the rolling tool 14 are rotatably connected to the toolcarrier 15 in the area of a rotating bearing 19, with the pliers-typebodies 17, 18 being coupled via a driving unit 20 provided here assingle-acting piston-cylinder unit and a distance between rolling areas21, 22 being reduced in dependence of a driving unit-side rotationalmovement of the pliers-type bodies 17 and 18 about the rotating bearing19. For this, the driving unit 20 is subject to hydraulic pressure and,under the action thereof, a piston element 23 is extended from acylinder element 24 of the driving unit 20, with a distance between theends 25 and 26 of the pliers-type bodies 17 and 18 facing away from therolling areas 21 and 22 being increased during such a change of theoperating state of the driving unit 20, while the distance between therolling areas 21 and 22 is decreased according to the geometricsituation in dependence of the rotary movement of the pliers-type bodies17 and 18 about the rotating bearing 19. The pliers-type bodies 17 and18 are each rotatably connected to the driving unit 20 in the area oftheir ends 25 and 26.

Furthermore, the two pliers-type bodies 17 and 18 are additionallyrotatably attached to the tool carrier 15 around the rotating bearing 19about a rotary axis 27 vertically aligned to the drawing plane to enablethe pliers-type bodies 17 and 18 to be swivelled upon contact of therolling areas 21 and 22 with a blade element 11 and avoid distortion ofthe blade elements 11 resulting from the contact of the rolling areas 21and 22 with the blade element. During joint rotation of the pliers-typebodies 17 and 18 around the rotating bearing 19 relative to the toolcarrier 15, the distance between the rolling areas 21 and 22 remainsconstant. Joint rotatability of the two pliers-type bodies 17 and 18around the rotating bearing 19 further ensures that the blade elements11, each of which being provided with a blade profile, areroller-compressible on their entire surface using the rolling tool 14.

The pliers-type bodies 17 and 18 are operatively connected to the toolcarrier 15 via piston elements 28 and 29, with the piston elements 28and 29 resetting the pliers-type bodies 17 and 18 relative to the toolcarrier 15 around the rotating bearing 19 to a zero position definedrelative to the tool carrier 15 and shown in FIG. 3 when a rotatingforce jointly rotating the pliers-type bodies 17 and 18 around therotating bearing 19 is essentially zero.

Furthermore, a resetting device 32, here including two spring-actiondevices 30 and 31, is associated to the pliers-type bodies 17 and 18through which the latter are rotated to enable a distance between therolling areas 21 and 22 to be changed to a maximum value.

Each of the rolling areas 21 and 22 here includes a ball element 33, 34retained in holding areas each and subjectable to hydraulic pressure inknown manner to enable the rolling pressure required in each case to beapplied to the blade elements 11 via the ball elements 33 and 34.

The holding areas 35 and 36 are here inserted into, and threadedlyconnected, preferably by means of grub screws, to adapter elements 37and 38 which are firmly threadedly connected to the pliers-type bodies17 and 18 and are at least approximately finger-shaped.

Each of the adapter elements 37 and 38 is changeable so that the rollingtool 14 provides for various engagement depths in the radial directionbetween the blade elements 11. Moreover, adapter elements 37 and 38designed with respect to the transmittable pressure or rolling force,respectively, are connectable to the pliers-type bodies 17 and 18, withthinner adapter elements being insertable into narrower areas betweenthe blade elements 11. Here, lower rolling or pressure forces,respectively, are applied to thinner blade elements 11 with more slenderadapter elements 37 and 38, with the adapter elements 37 and 38 thenhaving a certain elasticity and the maximum rolling force being limitedby the elasticity of the adapter elements 37 and 38. Full solidificationof the blade elements during compression rolling is avoidable bylimiting the maximum rolling force, with excessive pressure loadingduring roller compression producing a tensile stress maximum in thecenter area of the blade elements 11 which promotes internal crackformation under vibratory loading. This, however, is undesirable as itaffects the service life of the blade elements 11.

The rolling force imparted in each case to the rotor area during rollercompression is variable at each location of a blade element 11 and alsoin the transition areas 12 and the remaining surface 13 of the base body10 by controlling the hydraulic pressure applied to the rolling areas21, 22 via a pressure control unit not further shown in the drawing,thereby enabling the rotor area 9 to be solidified to the desired extentby producing the optimum residual compressive stresses required at eachlocation of the rotor area 9 and an improvement to be obtained withregard to the durability of the blades.

In order to facilitate, for example, CAD-CAM programming upstream of aroller compression process using the rolling tool 14 and subsequentimplementation of the manufacturing programs on a multi-axes machiningcenter by means of a post processor, an axis 39 of the carrier spindle16 in the operating state connected to the tool carrier 15 passesbetween the rolling areas 21 and 22 through a contact point present at adistance between the rolling areas 21 and 22 equal to zero. Thus, theaxis or the spindle carrier axis 29, respectively, and an axis throughthe contact point between the rolling areas 21 and 22 are congruent,thereby substantially facilitating programming.

In order to avoid damage to the blade elements 11 to be processed and tothe rolling tool 14 proper, a distance between the rolling areas 21 and22 is reducible via the drive unit 20 no further than to a defined limitvalue. Since the two ball elements 33 and 34 cannot be brought intocontact with each other by respective turning or swivelling of thepliers-type bodies 17 and 18 and, thus, the adapter elements 37 and 38,damage to the rolling tool 14 is prevented in a simple manner.

The rolling tool 14 enables integrally bladed disks and rotors of jetengines to be roller-compressed at low cost. The rapid and easy exchangeof the adapter elements 37 and 38 qualifies the rolling tool 14 with lowsetup times for use with rotor areas having different geometry, withdifferent engagement depths between blade elements as well as differentprocessing forces during the rolling process being representable ondifferently conceived components with high safety and processcapability.

The pliers-type design of the rolling tool 14 enables blade elements orairfoils, respectively, of one-piece rotor areas to be processed fromthe tip to the fillet, with simultaneous roller compression of thepressure and suction sides of blade elements being provided to avoiddistortion due to residual stress.

In addition, various individual tools enable the fillets or thetransition areas, respectively, between the surface of the bladeelements and the surface of the base body between the blade elements onthe suction and pressure side to be processed to the desired extent.Moreover, the surface of the base body between the blade elements or theannulus, respectively, is roller-compressible by means of individualtools.

Basically, the rolling tool 14 can be integrated into any knownmachining center. In contrast to resolidification by shot peening, thereis no need to procure expensive facilities. The rolling tool 14 enablesresolidification to be performed, for example, in conventional millingcenters. The milling centers are equipped with the rolling tool 14 andthe one-piece rotor areas are processed using the rolling tool 14 in thearea of their surfaces analogically to milling.

LIST OF REFERENCE NUMERALS

-   1 Jet engine-   2 Bypass duct-   3 Inlet area-   4 Fan-   5 Engine core-   6 Compressor arrangement-   7 Burner-   8 Turbine arrangement-   9 One-piece rotor area-   10 Annular base body-   11 Blade element-   12 Transition area-   13 Surface of the base body-   14 Rolling tool-   15 Tool carrier-   16 Carrier spindle-   17, 18 Pliers-type body-   19 Rotating bearing-   20 Driving unit-   21, 22 Rolling area-   23 Piston element-   24 Cylinder element-   25 End of pliers-type body 17-   26 End of pliers-type body 18-   27 Rotary axis-   28, 29 Piston element-   30, 31 Spring-action device-   32 Resetting device-   33, 34 Ball element-   35, 36 Holding area-   37, 38 Adapter element-   39 Axis

1. Method for the production of a one-piece rotor area, preferably a rotor area of a jet engine, with the rotor area including an annular base body and several, circumferentially distributed blade elements extending essentially radially from the base body, with residual stresses being imparted to the blade elements in surface-near areas by way of roller compression using a rolling tool introduced between the blade elements, with one each area of a blade element being arranged between areas of the rolling tool during roller compression, and with longitudinal sides of the blade element being simultaneously roller-compressed, characterized in that the rolling tool is radially introduced between the blade elements and the surfaces of the blade elements are roller-compressed.
 2. Method in accordance with claim 1, characterized in that the surfaces of the blade elements are roller-compressed by sequential radial traversing at least in certain areas.
 3. Method in accordance with claim 1, characterized in that the surfaces of the blade elements are roller-compressed by sequential axial traversing at least in certain areas.
 4. Method in accordance with claim 1, characterized in that the surfaces of the blade elements are roller-compressed by arbitrarily moving the rolling tool along the surfaces of the blade elements at least in certain areas.
 5. Method in accordance with claim 1, characterized in that the transition areas between the surfaces of the blade elements and the surface of the base body between the blade elements are roller-compressed using a rolling tool.
 6. Method in accordance with claim 1, characterized in that the surface of the base body between the blade elements is roller-compressed using a rolling tool.
 7. Method in accordance with claim 1, characterized in that the surfaces of several blade elements axially arranged one behind the other are roller-compressed.
 8. Method in accordance with claim 1, characterized in that a rolling force for setting a residual stress profile on the surfaces of the blade elements and/or the transition areas and/or the surface of the base body is variable between the blade elements.
 9. One-piece rotor area with an annular base body and several blade elements distributed over the circumference of the base body and extending essentially radially from the base body, characterized in that at least the blade elements feature a roller-compressed surface.
 10. One-piece rotor area in accordance with claim 9, characterized in that the transition areas between the surfaces of the blade elements and the surface of the base body between the blade elements feature a roller-compressed surface.
 11. One-piece rotor area in accordance with claim 9, characterized in that the base body features a roller-compressed surface at least in the area between the blade elements.
 12. One-piece rotor area in accordance with claim 9, characterized in that several blade elements axially arranged one behind the other on the base body are provided with a roller-compressed surface. 